You don't need a book. Just start your regular major scale on a note other than the root and BAM - you got modes.

But heads up, unless you have an application in mind that really calls for modal playing, modes are pretty much useless beyond scale drills. It's good to have them under your fingers, but 99% of the music you learn will be plain major or minor. Maybe if you learn a lot of Phish and Grateful Dead songs you'll use mixolydian and dorian.

Harmonizing all your modes is a good basic chord-building exercise, but it's not really something you'll get to apply directly to (most) music you play. Effective harmony is really based not based on scalar relationships per se.

Many songs use "modes as scales" (what I mean by that is, for example, they use the b7 accidental instead of a major 7th in a major song or a major 6th accidental instead of a minor 6th in a minor song). But they are not modal music and they are still in a key (modal music is not in a key). But I would concentrate more on harmony. Not what chords fit a scale but what notes fit a chord progression (hint: play chord tones). I mean if you have a chord progression in A minor like Am-D, you could say that it's a "dorian vamp." You would most likely play the notes in dorian scale over it (because of the major sixth - F# - that is in D major chord) and natural minor scale wouldn't even fit the chords. But it's still in a key. You are just using major 6th accidental and playing the chord tones.

To get a 'modal' sound, you take the notes of a scale and you pick a new root, while keeping the same notes.

For example: C major scale CDEFGAB
If you play Dmin|G, your progression will actually be D minor, but the notes you are using are still the same as a C major scale. This is possible because keys differ from scales.

But to look at it the right way: The D dorian scale is basically a D minor scale, but with the sixth degree raised a half step.

So basically what most people think are modes, are actually keys.

So don't say, my progression is D dorian, because that is not true in 99,9% of the cases. Say: My progression is in D minor with an accidental.

That way you can still have a 'modal' sound but you can explain what is going on correctly.

Modes are not important, keys are the most important thing.

Here is something you need to know to sound 'modal':

Ionian: Major
Dorian: Minor with a major sixth
Phrygian: Minor with a minor second
Lydian: Major with an augmented fourth
Mixolydian: Major with a minor seventh
Aeolian:Minor
Locrian: Shit you'll most likely never use. (minor scale with a diminished fifth, so no minor scale but a 'diminished' scale)

nobody actually says "it's in D minor with an accidental". it's just in D minor. no need to specify - a musician of any real skill will be able to tell when accidentals are in use.

if the composition exclusively uses the notes in the D dorian mode, it can be said to be "in D dorian" to clarify. but it's still really in D minor, because music is heard in keys, not modes.

to go into this a little more: it's in the key of D minor. it can be in the d minor scale and be specified to have an accidental (or the D dorian scale), but you'd never have to say that in the first place because music is very rarely that static.

scales and keys are too things that need to be separated, and keys in all scenarios supersede scales.

yeah, when I think Key I think of Root*, maybe quality. You can say something is D and it'll be very apparent whether it's major or minor. If there is a specific "modal" aspect I'd communicate that, but I wouldn't use mode as part of the key. Usually applies just to short vamp progressions.

Think about the blues: the chords are all dominants, but you'd never say "This is in A mixolydian, then D mixolydian, then E mixolydian".

Edit: To Clarify: Root of the Tonic chord - I kind of assume that if you're in an ad hoc playing situation most people can hear basic changes given a key. Really depends on situation.

yeah, when I think Key I think of Root, maybe quality. You can say something is D and it'll be very apparent whether it's major or minor. If there is a specific "modal" aspect I'd communicate that, but I wouldn't use mode as part of the key. Usually applies just to short vamp progressions.

Think about the blues: the chords are all dominants, but you'd never say "This is in A mixolydian, then D mixolydian, then E mixolydian".

key =/= root.

root deals with harmony, not with keys. tonic is the word we use for that, and, functionally, they're extremely different.

while it's true that one could say it's in D and listen to it to determine the quality, D pretty much always connotes D major, hard and fast. unless you're being told what the tonic is on a piece that is very obviously in a minor key (i.e. if you ask what the tonic is of beethoven's moonlight sonata, and get "C#" as answer), you'd never hear someone say D to refer to D minor.